What is the FBA file format?
An .fba file is a Fitbit OS App Package, the installable bundle a developer produces when building an app or clock face for Fitbit smartwatches like the Ionic, Versa, and Sense. Under the hood it is a .zip archive that nests several more archives together: the companion code that runs on the paired phone, one platform folder for each supported device model, and a manifest file. The app logic is written in JavaScript, but the build minifies and tree-shakes it with rollup.js, so what ends up inside the bundle does not match the original source.
The Fitbit SDK creates the file when a developer runs the build step, writing it to the project's ./build/ directory, usually as app.fba. From there it is either sideloaded onto a device for testing or submitted to the Fitbit App Gallery. Since Google acquired Fitbit, the SDK and its tooling are maintained under Google.
Security & safety
RISK: LOWAn .fba is a standard ZIP archive holding minified JavaScript and a manifest, with no native executable code that runs on a PC. The main caution is provenance: only install bundles from developers you trust, since an app you sideload runs on your watch. Extracting the archive to inspect it is safe.
Format details
in a nutshell- FlashBackup Archive - Some backup utilities have used .fba for a full backup archive file, unrelated to Fitbit.
- FontBase asset file - Occasionally cited as a font-management data file; unrelated to the Fitbit format.
Programs that open FBA files
Windows3 apps
Fitbit Command-Line Interface (@fitbit/sdk-cli)
Free Install Node.js, add @fitbit/sdk and @fitbit/sdk-cli to your project, then run npx fitbit and use the install command to push the .fba to a connected device or simulator.
Fitbit OS Simulator
Free Launch the desktop simulator and install the built .fba through the Fitbit shell to preview the app without hardware.
Any ZIP tool (7-Zip)
Open-source Rename the file to .zip or open it directly to inspect the manifest and nested platform folders inside the bundle. 
macOS3 apps
The Unarchiver
Free Extract the .fba as a ZIP to browse the companion code, platform ZIPs, and manifest.
Fitbit Command-Line Interface (@fitbit/sdk-cli)
Free Run npx fitbit from your project to open the shell, then use install to deploy the .fba to a paired device or the simulator.
Fitbit OS Simulator
Free Open the simulator and load the .fba via the shell to test the app on macOS. 
Linux2 apps
unzip
Open-source Run unzip app.fba to extract and examine the manifest and nested archives from a terminal.
Fitbit Command-Line Interface (@fitbit/sdk-cli)
Free With Node.js installed, run npx fitbit-build to produce the .fba and npx fitbit to install it onto a device or the simulator.
Fitbit Studio
Free Use the browser-based IDE to build a project and install the resulting .fba onto a paired device or the simulator. Technical details
deep spec| Encoding | Binary ZIP container |
| Byte order | N/A (ZIP is little-endian in its own fields) |
| Container | ZIP archive |
| Compression | DEFLATE (standard ZIP compression) |
| Encryption | None by default; distribution is gated through the Fitbit App Gallery |
| Structure | A single ZIP file that nests further ZIP archives: a companion bundle (code that runs on the paired phone), one platform ZIP per supported device model, and a manifest file describing the app or clock face. Application logic is written in JavaScript and is minified and tree-shaken during the build. |
| Integrity | Relies on the CRC-32 checks built into the ZIP format |
| Platforms | Fitbit OS |
| Notes | Produced by the Fitbit OS SDK when a developer runs the build step. The output is written to the project's ./build/ directory, usually as app.fba. Because the JavaScript is minified during bundling, the archive is not a substitute for the original source project. |
| Build Tool | Fitbit CLI (@fitbit/sdk-cli), invoked as npx fitbit-build; bundling and tree-shaking use rollup.js |
| Typical size | Tens to a few hundred kilobytes, depending on assets and target device count |
| Released | 2017 |
| Specification | dev.fitbit.com |
FBA conversions
Community Q&A
asked by usersNo questions yet - be the first to ask about FBA files.
